Simultaneous activity in the parallel fiber (PF) and climbing fiber (CF) synapses innervating cerebellar Purkinje cells causes a long-lasting depression (LTD) of transmission at the PF synapse. This LTD is a form of synaptic plasticity that may underlie certain forms of learning that occur in the cerebellum and is widely studied as an experimentally tractable example of long-lasting synaptic plasticity. The general goal of this project is to understand the molecular events that occur in postsynaptic Purkinje cells to produce LTD. The specific focus of the work is to study the roles of intracellular second messengers, such as IP3 and Ca ions, in inducing LTD and to understand how such messengers cause long-lasting changes in postsynaptic glutamate receptors. The proposed experiments combine electrical and optical methods to study these signaling pathways. Light-induced lease of Ca and IP3 from inert "caged" molecules will be used to elevate the concentration of these messengers very rapidly within small regions of the Purkinje cell. Simultaneous use of a high-speed confocal laser-scanning microscope will permit measurement of the consequences of these manipulations upon Ca concentration within the Purkinje cell and patch-clamp measurements will determine whether these messengers cause a LTD or PF synaptic transmission. Such experiments will define the roles of IP3 and Ca in LTD. Localized light-induced release of glutamate will also define, for the first time, the changes that occur in Purkinje cell glutamate receptors during LTD. This information will provide a molecular description of the final expression of LTD and give further clues about the coupling of second messenger pathways to glutamate receptors. Although this work is primarily basic research, it will yield new insights into basic signaling processes of neurons and synapses and will be useful for understanding the roles of such processes in the various neurological diseases that arise from defective neuronal signaling.